Large Isotope Shifts Research Articles

Oxygen isotope effect on the vibrational modes of Bi 2Sr 2CaCu 2O 8+δ

The 16O 18O oxygen isotope effect has been studied in the Raman spectra of single crystals of the high- T c superconductor Bi 2Sr 2CaCu 2O 8+δ. It is found that the oxygen isotope shifts of all of the vibrational peaks fall into one of three narrow ranges. The absence of a significant isotope shift for certain peaks indicates either that they correspond to normal modes that involve only the motion of cations (peaks at and below 181 cm −1), or that they involve the vibration of oxygen on sites where isotope exchange proceeds extremely slowly (peaks at 310 cm −1 and 661 cm −1). The isotope-shift data provide strong evidence that, contrary to previous assignments, the A 1g peaks at 287 cm −1 and 350 cm −1 correspond to vibrational modes of oxygen atoms in the copper layer. Large oxygen isotope shifts support the assignment of the 386 cm −1 peak to in-plane vibrations of oxygen atoms in the strontium layer, and of the 458 cm −1 peak to c-axis vibrations of these same atoms. They are inconsistent with an earlier suggestion that the 458 cm −1 peak corresponds to a vibrational mode of oxygen atoms in the copper layer.

A stable isotopic record of the Maastrichtian ocean-climate system: South Atlantic DSDP site 528

The upper Maastrichtian interval of mid-latitude South Atlantic Deep Sea Drilling Project site 528 spans approximately the last 4 million years of the Cretaceous. The isotopic record of this sequence indicates that relatively large (0.5–1.0%) late Maastrichtian oxygen and carbon isotopic shifts occurred on geologically short time scales (less than 100–500 kyr). Comparison with previous oxygen isotopic data suggests that in high- and mid-latitude southern oceans the multimillion-year Maastrichtian cooling trend largely resulted from geologically rapid climatic ‘steps’. Coincidence of the largest carbon and oxygen isotopic excursions suggests that relatively large and geologically rapid changes in marine and atmospheric carbon content may have directly contributed to the long-term cooling of the Late Cretaceous ‘greenhouse’.

Far-infrared properties of C60 and C70 compacts

The far-infrared transmission of polycrystalline C60 and C70 compacts has been measured from 3 to 330 cm−1 as a function of temperature. Both intrinsic and impurity-induced absorption bands are identified in these samples. The low temperature phase of C60 is observed to have two infrared active translational modes at 40.9 and 54.7 cm−1. Samples of C60 exposed to air before cooling to low temperatures contain several additional infrared bands which have been identified with adsorbed H2O vapor. A large isotope shift is observed for some of the bands when H2O is replaced by D2O, consistent with rotational or librational behavior. For C70 one strong intrinsic band is centered at 21 cm−1 and four much weaker bands occur at 28, 32, 52, and 64 cm−1. When doped with H2O vapor, C70 also produces several strong H2O impurity bands, some of which show isotopic shifts. The temperature dependence of five intramolecular C70 modes in the frequency range from 200 to 330 cm−1 is also reported.

Laser-induced fluorescence excitation spectra of indoline: low-frequency vibrations of the pseudo-four-membered ring

The laser-induced fluorescence excitation (FE) and single vibronic level luminescence (SVL) spectra of indoline have been studied by a pulsed seeded jet technique. The vibronic spectrum bears the signature of two low-frequency vibrations involving coupling of C2-puckering and N-inversion. A low-frequency (122 cm−1 regular progression in the FE spectrum has been assigned to a coupled vibration involving C2-puckering and N-inversion. The corresponding ground state frequency, as obtained from SVL spectra, is 160 cm−1. Another series of bands with irregular intervals has been fitted with a double-well potential barrier of 33 cm−1; this corresponds to the second coupled vibration fo C2-puckering and N-inversion. On substituting the H atom attached to the N atom by a D atom, a large isotope shift is obtained. This is explained as being due to a large difference in NH vibrational frequencies of S0 and S1 states.

Isotope effect in superconductivity on 13C substituted βH-(BEDT-TTF)2I3

We have investigated the resistive superconducting transition of βH-(ET)2I3 crystals in which the two inner carbon atoms, in the center of the ET molecule, have been substituted with 13C isotopes. We stabilised the βH state of (ET)2I3 at low temperature via the appropriate cooling procedure in a He gas pressure apparatus (“Orsay process”). The superconducting transition of 13C substituted samples was found to be Tc = 7.80±0.05 K (at midpoint), namely 0.20K lower than that of standard 12C samples (Tc = 8.0±0.1 K). We have taken care that both types of samples were measured in the same conditions and that p(T) data were free from cracks which can broaden the superconducting transition. This large and regular isotope shift of Tc is in contrast with most of the previous results in organic superconductors and suggests the existence of a superconductivity mechanism mediated by the coupling of electrons with the intramolecular phonom models.

Radiation detected resonance ionization spectroscopy on208Tl and242fAm

An ultra-sensitive laser spectroscopic method has been developed for the hyperfine spectroscopy of short-lived isotopes far off stability produced by heavy ion induced nuclear reactions at very weak intensity (> 1/s). It is based on resonance ionization spectroscopy in a buffer gas cell with radiation detection of the ionization process (RADRIS). As a first on-line application of RADRIS optical spectroscopy at242fAm fission isomers is in progress at the low target production rate of 10/s. The resonance ionization has been performed in two steps utilizing an excimer dye laser combination with a repetition rate of 300 Hz. The first resonant step proceeds through terms which correspond to wavelengths of 466.28, 468.17 or 426.56 nm; the second non-resonant step is achieved with the 351 nm radiation of the excimer laser itself, running with XeF. The frequency scans of the tuneable dye laser at 466.28 and 468.17 nm exhibit broad resonance ionization signals, the latter with a large isotope shift between242fAm and243Am which is in accordance with the large quadrupole moment of the242fAm fission isomer.

Highly structured singlet oxygen photoluminescence from crystalline C60.

Crystalline ${\mathrm{C}}_{60}$, after exposure to air, is shown to exhibit the characteristic luminescence spectrum of singlet molecular oxygen. The role of oxygen is verified by measuring the large isotope shift of the ${\mathrm{O}}_{2}$ vibrational mode luminescence replica in a sample prepared with $^{18}\mathrm{O}_{2}$. Detailed spectroscopy reveals novel bands in the spectrum which arise from vibronic coupling of the ${\mathrm{O}}_{2}$ transition to the ${\mathrm{C}}_{60}$ molecules. This allows measurement of the ${\mathrm{C}}_{60}$ vibrational spectrum with unparalleled sensitivity and precision from mg-sized samples.

Spectroscopic studies of jet-cooled CuAg

Resonant two-photon ionization spectroscopy has been applied to jet-cooled diatomic CuAg. Four band systems have been observed, three of which have been rotationally resolved and analyzed. The ground state is X 1Σ+ in symmetry, deriving from the 3d10Cu4d10Agσ2 molecular configuration. Its bond length has been determined as r0=2.3735±0.0006 Å (1σ error limits). Based on an analysis of the possible separated atom limits, three of the excited states observed (A 0+, A′ 1, and B′ 0+ ) are assigned as primarily 3d9Cu4d10Agσ2σ* in character. The observation of unusually large electronic isotope shifts in the A–X, A′–X, and B′–X band systems, similar in magnitude to those previously observed in the A–X and B–X systems of Cu2 and the s←d excitations in atomic copper, provides further confirmation that these excited states derive from the 3d9Cu4d10Agσ2σ* molecular configuration. Finally, the highest energy state observed in this work is argued to be primarily ion pair in character, and is expected to have significant contributions from both the Cu+Ag− and Cu−Ag+ ion pair states.

Measurements of isotope shifts of accelerator-produced radioactive atoms in an on-line resonance cell

Fluorescence spectra from atoms of radioactive nuclides produced by heavy-ion fusion reactions have been measured on line with a gas-filled, liquid-nitrogen-cooled resonance cell. This device yields useful spectra from Yb nuclides produced at rates lower than 1000 s −1. Spectra have now been obtained for Yb isotopes more than 18 neutrons away from the line of β stability. These data show a large isotope shift surprisingly near the N = 82 shell closure. The apparatus has also been used to measure isotope shifts of the refractory element Hf.

Incoherent neutron scattering in acetanilide and three deuterated derivatives.

Incoherent-neutron-scattering measurements of the vibrational density of states of acetanilide and three deuterated derivatives are presented. These data allow one to identify an intense maximum, assigned to the N-H out-of-plane bending mode. The data display the specific behavior of the methyl torsional modes: large isotopic shift and strong low-temperature intensity; confirm our previous inelastic-neutron-scattering studies, indicating no obvious anomalies in the range of frequency of the acoustic phonons. In addition, the data show the existence of thermally activated quasielastic scattering above 100 K, assigned to the random diffusive motion of the methyl protons. These results are discussed in the light of recent theoretical models proposed to explain the anomalous optical properties of this crystal.

Metal isotope effects on the vibrational spectra of (bis(glycylglycinato)calcium chloride)n.

The infrared and Raman spectra of [bis(glycylglycinato)calcium chloride]n and its isotopic complexes containing metal and hydrogen isotopes have been measured. A large isotope shift of more than 4 cm-1 on 40Ca and 44Ca substitution has been observed in the infrared-active bands at 345, 267 and 242 cm-1. These bands have been assigned to Ca-O antisymmetric stretching vibrations. The Raman-active bands at 305, 158 and 111 cm-1 have been assigned to Ca-O symmetric stretching vibrations with no displacement of the calcium atom. The result of a normal coordinate analysis is consistent with both the empirical assignments and the experimental isotope shifts. These results indicate that Ca-ligand bond forces are almost similar to those of copper- and zinc-amino acid complexes.

A preliminary study on the chemical and isotopic characteristics of geothermal waters and gases in northern Thailand.

Hydrogen and oxygen isotopic compositions of hot spring waters and meteoric waters from San Kamphaeng, Fang, and their vicinity in northern Thailand were measured. Although most of the data fall on the global meteoric water line δD=8δ18O+10, some meteoric waters exhibit high δD and δ18O values which plot on a different line defined by δD=8δ18O-5. The isotopic compositions of hot spring waters vary in the range defined by the above meteoric water lines with the δD variation between -50 and -62‰. No large oxygen isotopic shift was observed for all geothermal waters collected in this survey, indicating that the geothermal waters originate from the local meteoric waters.A distinct difference was observed in hydrogen concentrations of soil gases between San Kamphaeng and Fang geothermal areas. In Fang the high H2 concentration areas are distributed around the hot spring zone and a closed fluorite mine which is a product of past hydrothermal activity. No such areas were found in the San Kamphaeng area, suggesting that geothermal activity may be higher in Fang than in San Kamphaeng.The 3He/4He ratios of helium in hot spring gas samples from the Fang area are higher than those from the San Kamphaeng area, although these values are lower than 3×10-7. The δ13C values of CO2 in these hot spring gas samples (-7 to -11‰) are close to those for volcanic CO2. This suggests that the volcanic CO2 is supplied from the deep seated geothermal system and a possibility that mantle He is diluted by a large amount of crustal He originated from abundant radioactive elements in granitic rocks widely distributed in northern Thailand.

Laser excitation spectroscopy of the A and B states of jet-cooled copper dimer: Evidence for large electronic isotope shifts

Fluorescence excitation spectra recorded for the A–X system of jet-cooled Cu2 show conclusive evidence of a ΔΛ=0 transition, and the A state is thereby definitively assigned as 1Σ+u. A previous assignment of the B state as 1Σ+u is confirmed, but the vibrational levels of this state are complicated by the presence of a perturbation at v′=0. The perturbing state does not, however, appear to be either of the two optically accessible electronic states in this spectral region. Anomalously large electronic isotope shifts are observed for the A and B states, and this behavior is discussed in terms of the correspondingly large ‘‘specific mass shifts’’ observed in the optical spectra of atomic copper for transitions that couple states differing in the number of d electrons. Due to the large spin-orbit coupling constants in the ‘‘d-hole’’ configurations, it is proposed that the low-energy-excited molecular states of Cu2 derived from these configurations should be described by Hund’s case (c) coupling. Dynamical effects observed in the gas phase and in solid matrices are briefly discussed in terms of this bonding scheme.

Is the large oxygen isotopic Tc shift in YBa2Cu3Ox intrinsic?

It is suggested that the extremely large oxygen isotopic Tc shift recently reported in YBa2Cu3O7 may not be an intrinsic mass effect related to the mechanism but due to the small difference of the oxygen contents.

Vibrational spectroscopy of acceptor-hydrogen complexes in silicon: Evidence for low-frequency excitations.

The infrared spectra of acceptor-H centers in passivated Si for B, Al, and Ga provide evidence for an unexpected low-frequency excitation of the complexes. The broad vibrational bands observed near 2000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at room temperature shift to higher frequency and narrow dramatically upon cooling to He temperature. While the B-H--related band remains structureless at intermediate temperatures, the vibrational bands observed for Al-H and Ga-H complexes show thermally populated sidebands to the low-energy side of the main vibrational bands. The sidebands indicate the presence of a low-frequency excitation of the complex. We have determined Boltzmann energies of 78 and 56 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ from the intensity of the sidebands as a function of temperature for Al-H and Al-D complexes, respectively. The absence of an anomalously large isotope shift is consistent with this excitation being due to an ordinary vibration rather than a tunneling splitting as is sometimes observed for hydrogen-containing complexes.

Large intrinsic nuclear magnetic resonance isotope shifts associated with bending motion along the bridging coordinate in carbocations

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLarge intrinsic nuclear magnetic resonance isotope shifts associated with bending motion along the bridging coordinate in carbocationsDavid A. Forsyth, James H. Botkin, James S. Puckace, Kenneth L. Servis, and Robert L. DomenickCite this: J. Am. Chem. Soc. 1987, 109, 24, 7270–7276Publication Date (Print):November 1, 1987Publication History Published online1 May 2002Published inissue 1 November 1987https://doi.org/10.1021/ja00258a004RIGHTS & PERMISSIONSArticle Views284Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (935 KB) Get e-Alerts Get e-Alerts

ChemInform Abstract: Isotope and Temperature Dependence of Transition‐Metal Shielding in Complexes of the Type M(XY)6

The temperature coefficients of the chemical shift of /sup 51/V in carbonyl complexes in solution are reported here. For transition metal nuclei the effects of rovibrational averaging can be obtained from these temperature coefficients without gas-phase studies in the zero-pressure limit. They present a theory for the large temperature coefficients and large isotope shifts observed in transition metal complexes. They use the vibrational analysis of V(CO)/sub 6//sup -/ and Co(CN)/sub 6//sup 3 -/ to provide dynamic averages of the displacements in the V-C, C-O, Co-C, and C-N bonds as typical examples. The temperature and mass dependencies of these dynamic averages successfully account for the signs and magnitudes of the observed temperature coefficients and isotope shifts. They report observations of a correlation between the temperature coefficients and chemical shifts. This correlation is qualitatively consistent with a simple electrostatic model for shielding. The limitations of the electrostatic model for shielding are discussed.

The oxygen-18 isotope shift in nitrogen-15 NMR spectroscopy. 3. Effects of structure and solvent

Various /sup 15/N, /sup 18/O-labeled compounds were synthesized and the /sup 18/O-induced isotope shifts on their /sup 15/N NMR spectra were measured in order to examine the effects of structural changes on the magnitudes of the shifts. The measured shifts vary greatly, ranging from 0.027 ppm for a nitrile oxide to 0.159 ppm for an isoxazole. The large isotope shifts of isoxazoles compared to oximes and isoxazoline are attributed to the aromatic nature and shorter N-O bond lengths of the isoxazoles. The nature of substituents in the para position of some aromatic aldehyde and ketone oximes affects the magnitude of the /sup 18/O-induced shift. Intramolecular hydrogen bonding significantly decreases the magnitude of the isotope shift in oximes. A study of the effect of solvents on the isotope shifts of three oximes is made. A significant decrease in the isotope shift is observed in solvents having an electron donor atom such as oxygen or nitrogen. This decrease in the magnitude of the isotope shift is ascribed to the formation of hydrogen bonds between the oxime hydroxyl proton and the oxygen or nitrogen of the solvent. Possible applications of the /sup 18/O isotope in /sup 15/N NMR are briefly discussed.

Rare earth element transport in the western North Atlantic inferred from Nd isotopic observations

The isotopic composition of Nd in the water column from several western North Atlantic sites and formational areas for North Atlantic Deep Water shows extensive vertical structure at all locations. In regions where a thermocline is well-developed, large isotopic shifts (2 to 3 ϵ units) are observed across the base of the thermocline. Regions without a thermocline are characterized by much more gradual shifts in isotopic composition with depth. In general, the data reveal an excellent correlation between the Nd isotopic distribution in the western North Atlantic water column and the distribution of water masses identified from temperature and salinity characteristics. NADW, as identified from T-S properties, is also characterized by a well-defined isotopic composition having ϵ_(Nd)(0) = −13.5 ± 0.5. This signature is associated with waters identified as NADW from high latitudes near formational areas in the Labrador Sea down to the equatorial region. The isotopic signature of NADW would appear to be formed by a blend of more negative waters originating in the Labrador Sea (ϵ_(Nd)(0) < −18) and more positive waters originating in the overflows from the Norwegian and Greenland Seas (ϵ_(Nd)(0) ≈ −8 to −10) and is consistent with classical theories on the formation of NADW. The isotopic signature of NADW is propagated southward to the equator where it is gradually being thinned out by mixing from above and below with more radiogenic Nd associated with northward-spreading Antarctic Intermediate and Bottom Waters. The preservation of the isotopic signature of NADW over these large distances indicate that the REE undergo extensive lateral transport. The isotopic composition of Nd is largely conservative over the time scales of mixing within the Atlantic in spite of the intrinsic nonconservative behavior of neodymium. Nd concentration gradients generally show surface waters to be depleted in Nd relative to deep waters, which must require vertical transport processes. However, isotopic differences in the water column preclude the local downward transport of REE from the surface into underlying deep waters as a simple explanation of the concentration gradient. The apparent decoupling of REE in NADW from overlying (local) surface waters and the increasing concentration with depth provide a conflict with simple vertical transport mechanisms that is not yet resolved.

Isotope and temperature dependence of transition-metal shielding in complexes of the type M(XY)6

The temperature coefficients of the chemical shift of /sup 51/V in carbonyl complexes in solution are reported here. For transition metal nuclei the effects of rovibrational averaging can be obtained from these temperature coefficients without gas-phase studies in the zero-pressure limit. They present a theory for the large temperature coefficients and large isotope shifts observed in transition metal complexes. They use the vibrational analysis of V(CO)/sub 6//sup -/ and Co(CN)/sub 6//sup 3 -/ to provide dynamic averages of the displacements in the V-C, C-O, Co-C, and C-N bonds as typical examples. The temperature and mass dependencies of these dynamic averages successfully account for the signs and magnitudes of the observed temperature coefficients and isotope shifts. They report observations of a correlation between the temperature coefficients and chemical shifts. This correlation is qualitatively consistent with a simple electrostatic model for shielding. The limitations of the electrostatic model for shielding are discussed.